1. Field of the Invention
The present invention relates to a method for manufacturing a plasma display panel suitable as a flat display panel, more particularly to a method for manufacturing a plasma display panel designed to shorten the time required to exhaust impurity gas that has been adsorbed into a substrate.
2. Description of the Related Art
According to a conventional method, when a color plasma display panel (hereinafter referred to as a xe2x80x9ccolor PDPxe2x80x9d) is manufactured, a scanning electrode, a sustaining electrode and the like are formed on a glass substrate so as to form a front substrate, and a data electrode and the like are formed on another glass substrate so as to form a rear substrate, and thereafter the front and rear substrates are sealed up by a continuous furnace in the atmosphere. Gases are then exhausted from a discharge space formed between the substrates by sealing. FIG. 1 is a graph showing change of temperature in a conventional method for sealing a color PDP, and FIG. 2 is a graph showing change of temperature in an exhaust process after the color PDP is sealed up by the conventional method.
In a conventional sealing method, a glass frit is first applied onto the edge of a rear substrate, and a front substrate is laid thereon. Thereafter, in a furnace that is filled with atmosphere, the temperature thereof is raised to 450xc2x0 C. in 1.5 hours as shown in FIG. 1, thereafter is maintained for 30 minutes at 450xc2x0 C., and is lowered to a normal temperature in about 3.5 hours. The glass frit is melted and solidified through the thermal treatment, so that the front and rear substrates are sealed up, and a panel structure of a color PDP is formed.
Thereafter, an exhaust pipe pre-connected to the rear substrate is connected to an exhaust system that has a vacuum pump and the like, thereby exhausting gas from the panel structure, and heating (baking) the panel structure. As a result, the moisture and gas that have been adsorbed in a protective film made of a MgO film and the like are removed. The heating (baking) process is carried out to activate MgO (i.e., to decompose magnesium hydroxide), and, in consideration of the melting point of the glass frit for sealing, the temperature thereof is roughly 380xc2x0 C., and the time period is 15 to 25 hours as shown in FIG. 2. Gas cleaning is also carried out by introducing a cleaning gas into the panel structure while being heated as shown in FIG. 2. Further, the discharge space is filled with a discharge gas after the temperature is lowered, thereby completing the color PDP.
However, in the manufacturing method, just when the gas begins to be exhausted through the exhaust pipe of the panel structure after they are sealed up, the front and rear substrates are pressurized by the atmospheric pressure, and an exhaust passage in the panel structure is pressed, and therefore conductance decreases. Further, since the gas is exhausted outside through the exhaust pipe, conductance in a piping system as well as in the panel structure is low. This lengthens the heating/exhausting time required to exhaust the impurity gas, which has been removed by baking, so as to clean the panel. Further, in a recently developed PDP, there is a case in which a closed cell structure in which each discharge cell is partitioned by ribs is employed to prevent interference of discharge between the discharge cells. However, in this structure, the exhaust passage in the panel structure becomes extremely small. Therefore, the time required to carry out the baking process and to exhaust the impurity gas is lengthened more than in a conventional PDP having a stripe cell structure, thus obstructing the productivity of the PDP considerably. Further, since a phosphor layer is heated in a vacuum for a long time proportionate to the lengthened exhausting/baking time, the phosphor layer is greatly damaged.
For these reasons, a PDP manufacturing method has been proposed for exhausting gases accumulating in the panel structure in a short time (Japanese Unexamined Patent Publication No. Hei 9-251839). According to the conventional manufacturing method described in this publication, a sealing agent is first applied onto one of two glass substrates, and these glass substrates are spaced out in a chamber. Thereafter, the glass substrates are degassed by heating them and carrying out vacuum evacuation of the chamber, and, under this state, one of the glass substrates is mechanically laid on the other glass substrate. Thereafter, the sealing agent is melted by further raising the temperature, and the glass substrates are sealed up with the sealing agent by lowering the temperature. A discharge gas is introduced through a chip tube pre-connected to one of the glass substrates before carrying out vacuum evacuation, or is introduced by filling the chamber with the discharge gas.
However, in the conventional manufacturing method described in Japanese Unexamined Patent Publication No. Hei 9-251839, the glass substrates as a pair, which are placed separately from each other in the chamber, are baked, and the glass substrates should be mechanically laid on each other. Therefore, structure and control for positional adjustment or similar adjustment are largely complicated, and, disadvantageously, costs rise. Further, since the procedure from the sealing step to the gas filling step is continuously performed, the exhaust pipe is connected to a discharge gas introduction mechanism disposed outside the chamber after the glass substrates are disposed in the chamber, or the chamber is filled with the discharge gas. In the method for connecting the exhaust pipe to the discharge gas introduction mechanism, the structure and control of a sealing device are further complicated. On the other hand, in the method for filling the chamber with the discharge gas, the amount of consumption of the discharge gas becomes extremely large, and a great disadvantage in cost exists. Further, since the pressure in the chamber becomes larger than the atmospheric pressure, it is needed to take measures against using the chamber as a container which endures an internal pressure, and a disadvantage also exists on equipment.
It is an object of the present invention to provide a method for manufacturing a plasma display panel capable of shortening the exhausting time of impurity gas without complicating the structure of a sealing device and its control.
A method for manufacturing a plasma display panel according to the present invention comprises the steps of: laying a front substrate and a rear substrate on each other with a sealing frit therebetween; heating the front substrate, the rear substrate and the sealing frit in a chamber and exhausting impurity gas from both of the substrates by lowering internal pressure of the chamber; melting the sealing frit in the chamber by further heating the front substrate, the rear substrate and the sealing frit; and solidifying the sealing frit in the chamber and sealing up the front substrate and the rear substrate.
In the present invention, the front and rear substrates are laid on each other with the sealing frit therebetween, and the impurity gas is exhausted. After the impurity gas is exhausted, the substrates are sealed up merely by melting and solidifying the sealing frit in the same chamber. Therefore, a positional adjustment between the front and rear substrates can be easily made without complicating the structure of the sealing device. In other words, since the front and rear substrates are laid on each other and are fastened, i.e., since the substrates have no need to be moved by a carrying device or the like, the structure of the sealing device and the control thereof including the chamber in which thermal treatment and the like are carried out are not required to be complicated when the impurity gas is exhausted. Further, since the impurity gas is exhausted while lowering the internal pressure of the chamber, the impurity gas easily flows out from between the substrates. At this time, since the space between the substrates is not completely sealed up by the sealing frit, the impurity gas is exhausted from therebetween as well as from the chip tube. Therefore, sufficient exhaust conductance is obtained.